New physics searches with charm decays at LHCb

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The goal of particle physics is to understand the fundamental building blocks of the universe and the rules by which they play. Some of these fundamental particles can be studied in nature---for example, all of the matter on earth is made from two kinds of quark (assembled into protons and neutrons) plus electrons. The nuclear furnace at the heart of the sun spits out immense numbers of neutrinos. Still other, rarer particles arrive in cosmic showers. All of the particles that we have found in nature, plus others that we have been able to produce in super-colliders, are described by a theory known as the Standard Model. This is a venerable theory that has stood, largely unmodified, since the 1970s. However, more and more evidence is piling up that the Standard Model is incomplete---that it is a good approximation but is missing some vital pieces, just as Newton's laws of motion were nearly right most of the time but were superseded by Einstein's theory of relativity. There are many aspects of the universe that the Standard Model does not explain, such as why matter is so much more common than anti-matter, or the nature of dark matter and dark energy (which together make up 95% of the universe!), or even gravity itself. There are also problems of internal consistency in the model. Many of these problems point to something new, exciting, and not at all understood just over the horizon; we simply call this 'new physics'. One powerful way to grapple with this is to look for things that the Standard Model says are impossible, but which are plausible with new physics. Then, if you see the supposedly impossible effect, you learn immediately that the Standard Model is wrong and---even more valuable---how it went wrong. If you don't see anything, that is still useful information: models of new physics now have to explain why the effect is not allowed, pinning them down. In this project, we will study a specific kind of particle known as charmed mesons. These particles are made from one charm quark and one light antiquark. They also have an antiparticle, made from one charm antiquark and one light quark. Both kinds are unstable, but can live for long enough to travel a fraction of a centimeter. In the Standard Model, there is a virtually perfect mirror symmetry between the two: they live for the same amount of time on average, they decay in equivalent ways, and so on. With new physics, though, this symmetry can be broken. The effect is very slight, so we need to study enormous numbers of particles to see it. We will do this with the data recorded by the LHCb detector at the Large Hadron Collider, which will begin operation in 2008. LHCb will record hundreds of millions of charm meson decays, a vastly larger sample than we've had access to before. By sifting through this data, we hope to find this slight discrepancy, break open the Standard Model, and finally uncover the new physics that lies beyond.